The demand for less expensive, lower power and more reliable integrated circuit components for use in communication, imaging and high-quality video applications continue to increase rapidly. Digital signal processors (DSPs) find wide use and acceptance in such applications, including in cell phones, PDAs, hearing aids, and many other devices including those processing audible sounds.
In DSP systems, analog signals are typically converted into a digital format for processing, and then these processed digital signals are converted back to analog signals. A codec device is often used at a front-end of a DSP, which integrates analog to digital and provides digital to analog conversions.
As shown in FIG. 1 at 10, a specific type of DAC, commonly known as a sigma-delta DAC shown at 12, is utilized to modulate input signals and provide a 3-level DIN output having outputs +1, 0, and −1. These DIN outputs may be provided to an H-bridge 14. The H-bridge 14 typically operates from voltage sources V+ and V−, and provides analog outputs Vout P and Vout M.
In conventional designs, the common-mode noise level at the output of the H-bridge is significant. The common-mode output in this conventional design is ((V+)+(V−))/2 when the DIN is +1 or −1, and V− or V+ when DIN is 0, depending on which 0 state is chosen. This leads to a high, common-mode noise level at the output of the H-bridge.
There is desired circuitry to reduce common-mode noise levels at the output of an H-bridge, particularly when processing DIN inputs −1, 0, and +1 from a 3-level sigma-delta modulator.